| Fuel ethanol,as an environment-friendly and sustainable energy source,has attracted more and more attentions in recent years.The production of ethanol from fermentation of syngas has become a very promising unique technology.At present,the low gas-liquid mass transfer is one of the main obstacles.In this thesis,we designed the tower reactor,and explored and optimized the conditions of ethanol fermentation with it.The results are as follows.Experiment with strain C.autoethanogenum DSM10061 as the research object.Through comparison of synthesis gas fermentation ethanol concentration under the different number of different trays(0,1,2,3,4,5,6,7)in the tower reactor.It was found that increasing the tray could promote the growth of bacteria in the fermentation broth,and also promoted the production of ethanol.The test results show that,when the number of trays was 5,the concentration of bacteria reached the maximum OD600 was 0.271 on the 5th day,the ethanol concentration was 310.023mg/L,the syngas consumption rate in the fermentation process was H2 92.4%,CO 64.11%,CO285.84%.With reactor of the number trays was 5 for the further test,to discuss the effects of cycle interval time on ethanol fermentation.The results show,bacterial strain C.autoethanogenum DSM10061 grows the most exuberant,and it’s concentration was up to 0.673,ethanol concentration reached the highest 484.563 mg/L,the maximum gas consumption rate was H2 93.11 %,CO 64.18%,CO2 86.97 % under the condition of fermentation broth was returned once every 8 h.Based on the above conditions,we fill gas intermittently in the culture medium.The bacteria growth and fermentation is better when gas is filled every 4 days.The OD600 and ethanol concentration could achieve 0.472 and 581.82mg/L respectively.The maximum consumption rate of H2,CO and CO2 are85.62%,40.95%,65.39%.With above optimum parameters,we fermented the ethanol in the reactor with different liquid volumes(500 and 1000 m L).The results showed that the ethanol concentration fermented from syngas in a liquid volume of 500 m L is higher than that in a liquid volume of1000 m L,which could achieve a maximum value of 603.92mg/L,increased 1.8 times and 2.5 times respective In this condition,the maximum OD600 of bacteria growth was 0.549 and H2 85.73%,CO41.08%,and CO2 68.71% in the syngas were consumed.The optimum parameters of the reactor were summarized,and the optimum conditions of the reactor were as follows: 5 trays,each 8h circulation reflux,every 4d intermittent gas,500 ml reactor liquid loading.Three strains C.autoethanogenum 、 C.ljungdahlii and A-fm4 were used to compare the parameters of the reactor.The results showed that the fermentability of c.autoethanogenum was stronger than c.ljungdahlii and A-fm4,the maximum OD600 of bacteria growth was 0.548,the maximum ethanol production was 620.56 mg/L,and the maximum consumption rate of H2,CO and CO2 was 87.92%,41.46% and 70.8% in the fermentation process respectively.In conclusion,our results confirm that the tower reactor can enhance the mass transfer between the syngas and fermentation broth medium and thereby can improve the production of ethanol.This provides experimental ideas and theoretical basis for further exploration of the method to increase the gas-liquid mass transfer efficiency in the anaerobic fermentation of syngas. |
PDF Full Text Request